1. Field of the Invention
The present invention relates to a backlight driving apparatus and a liquid crystal display (LCD) device using the same, and more particularly, to a backlight driving apparatus and an LCD device using the same, which can minimize a loss of power to enhance power conversion efficiency.
2. Discussion of the Related Art
Backlights are devices that irradiate light on a display panel, and use a cold cathode fluorescent lamp (CCFL) as a light source. However, when the CCFL is used, a harmful environment is caused by mercury, a response time to an applied signal is slowed by about 15 ms, and a color reproducibility is lower by about 75% with respect to standards published by the National Television Standard Committee (NTSC). Also, the CCFL causes other problems such as predetermined white light being emitted. For this reason, recently, light emitting diodes (LEDs) are drawing much attraction as a light source.
In comparison with CCFLs, LEDs are eco-friendly, are quick to respond with a response time of several nano seconds, are driven with an impulse, and have a color reproducibility of 80% to 100%. Also, in backlights using the LEDs, a luminance and a color temperature can be arbitrarily adjusted by adjusting an amount of light.
FIG. 1 is a diagram for describing a general backlight driving apparatus.
As illustrated in FIG. 1, the general backlight driving apparatus includes a DC-DC converter 20 that supplies a driving voltage Vd to a light source 10, a feedback circuit 30 that detects a voltage level of the driving voltage Vd to feed back the detected voltage level to the DC-DC converter 20, and a duty controller 40 that controls a turn-on/off of the light source 10 according to a backlight dimming signal DIM supplied from the outside.
The light source 10 includes a plurality of LED arrays LA1 to LAn in which a plurality of LEDs are serially connected to each other. Each of the plurality of LED arrays LA1 to LAn emits light with a current which flows according to the driving voltage Vd supplied from the DC-DC converter 20.
The DC-DC converter 20 generates the driving voltage Vd on the basis of an input voltage Vcc supplied from the outside, and supplies the driving voltage Vd to the plurality of LED arrays LA1 to LAn, thereby emitting light from the LEDs of each of the plurality of LED arrays LA1 to LAn.
The feedback circuit 30 voltage-divides the driving voltage Vd outputted from the DC-DC converter 20 to generate a feedback voltage Vfb by using first and second resistors R1 and R2 which are serially connected to each other, and feeds back the generated feedback voltage Vfb to the DC-DC converter 20. Thus, the DC-DC converter 20 generates a pulse width modulation (PWM) signal corresponding to the feedback voltage Vfb supplied from the feedback circuit 30, and turns on a switching element according to the PWM signal to output the driving voltage Vd which has a voltage level equal to or higher than a certain voltage level with respect to the input voltage Vcc.
The duty controller 40 is connected to the light source 10, namely, the plurality of LED arrays LA1 to LAn, and controls a turn-on/off period of the plurality of LED arrays LA1 to LAn according to the backlight dimming signal DIM to adjust a brightness of the light source 10. Therefore, the plurality of LED arrays LA1 to LAn emit light during a duty-on section of the backlight dimming signal DIM.
However, the general backlight driving apparatus has the following problems.
First, since the switching element of the DC-DC converter 20 is turned on even during a duty-off section of the light source 10, a loss of power such as a switching loss of the switching element occurs, causing a reduction in power conversion efficiency.
Second, the plurality of LED arrays LA1 to LAn are repeatedly turned on/off by the backlight dimming signal DIM to continuously change a load condition of the DC-DC converter 20, and a load condition of the turn-on period of the LED arrays LA1 to LAn differs from that of the turn-off period of the LED arrays LA1 to LAn. For this reason, it is difficult to maintain a constant power conversion efficiency of the DC-DC converter 20.